Lumbar spinal canal stenosis is a disease in which the spinal canal is stenosed due to recession degeneration of intervertebral discs and ligaments, and can cause symptoms such as back pain, leg pain, and intermittent claudication. In order to treat the lumbar spinal canal stenosis, surgery for partially resecting the spine in a site causing the stenosed spinal canal (laminectomy) or a surgery for fixing the spine (spinal fusion surgery) can be performed. In contrast, as a surgical technique, which is relatively minimally invasive compared to the laminectomy or the spinal fusion surgery, a method, has been recently developed in which a metallic spacer is caused to indwell between spinous processes so as to release compression of spinal nerves or nerve roots. However, according to the method, it is necessary to resect back muscles and ligaments in order to cause the spacer to indwell. Consequently, a patient still feels that the surgery is very invasive, and can require longer medical treatment.
In order to solve this problem, an alternative method has been proposed in which a spacer is inserted into and caused to indwell between the spinous processes in a less invasive manner. For example, as the alternative method, U.S. Patent Application Publication No. 2009/0118833 discloses a method of using a dilatable balloon as the spacer. In this case, the balloon in a folded state is percutaneously inserted into the spinous processes. The inside of the balloon is filled with a filling material such as bone cement, and the balloon is dilated and caused to indwell the spinous processes. The filling material is cured after filling the balloon, and thus the balloon can semi-permanently maintain a dilated state.